1. Field of the Invention
The present invention generally relates to a horizontal synchronizing signal separator which separates a horizontal synchronizing signal from a video synchronizing pulse signal for use in video signal processing.
2. Description of the Prior Art
In the transmission of a video signal based on a standard television system, a video synchronizing pulse signal comprising a horizontal synchronizing pulse signal, a vertical synchronizing signal and an equalizing pulse signal is inserted in the video signal during its flyback-line blanking time; while, on the side of video signal reception, the video synchronizing pulse signal is extracted from the received video signal and the horizontal and vertical synchronizing signals are separated from the video synchronizing pulse signal as the processing of the video signal.
Explanation will be made as to the separating operation of a horizontal synchronizing signal from a video synchronizing pulse signal in a prior art horizontal synchronizing signal separator, by referring to FIG. 3.
In FIG. 3, reference numeral 1 denotes a video synchronizing pulse signal which comprises a horizontal synchronizing pulse signal 1a, an equalizing pulse signal 1c, a vertical synchronizing pulse signal b, the equalizing pulse signal 1c, . . . , sequentially arranged from the left side in the drawing. Each of these signals 1a, 1c, 1b are assumed to have a train of 6 consecutive pulses, though partly omitted in the drawing. Reference numeral 2 denotes a pulse signal which is generated from, e.g., a monostable multivibrator for the purpose of obtaining the horizontal synchronizing signal from the video synchronizing pulse signal 1, while reference numeral 3 denotes a pulse signal which is generated from the monostable multivibrator when there is a missing pulse in the video synchronizing pulse signal 1.
In the case where such a video synchronizing pulse signal 1 based on the standard television system as shown in FIG. 3 is employed, generally speaking, if the horizontal synchronization has a period of H, then the horizontal synchronizing pulse signal 1a has a period of H and the vertical synchronizing pulse signal 1b and the equalizing pulse signal 1c have respectively a period of H/2.
Thus, when it is desired to separate a horizontal synchronizing signal from the video synchronizing pulse signal 1, such a pulse signal 2 that rises when a leading or front edge in each period H of the video synchronizing pulse signal 1 is detected and falls in a time shorter than the period H of the horizontal synchronizing signal is generated from a pulse signal generating means such as a monostable multivibrator.
And the rising edges of the pulse signal 2 are handled as the horizontal synchronizing signal obtained through separation from the video synchronizing pulse signal 1.
With the aforementioned prior art horizontal synchronizing signal separator, however, in the case where the video synchronizing pulse signal 1 is obtained from a special reproduction image signal of a video tape recorder, if such a pulse missing takes place in the equalizing pulse signal 1c as shown by an arrow A in FIG. 3, then the pulse signal obtained through detection of the front edge of the video synchronizing pulse signal 1 corresponds to the pulse signal 3 having a period shifted by a phase of H/2 in its part subsequent to the pulse missing position of the equalizing pulse signal 1c.
And the pulse signal 3 once subjected to such a phase shift cannot be returned to its original normal phase until the next front edge of the horizontal synchronizing pulse signal 1a is detected. Therefore, such a problem occurs that the horizontal synchronization remains disturbed during a time duration between the pulse missing position of the equalizing pulse signal 1c and the detection of the next front edge of the horizontal synchronizing pulse signal 1a.